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Matter: Its Properties, States, Varieties, and Behaviour
Structures of metals.
The elements are found in a variety of crystal packing arrangements.
The most common lattice structures for metals are those obtained by stacking the atomic spheres into the most compact arrangement. There are two such possible periodic arrangements. In each, the first layer has the atoms packed into a plane-triangular lattice in which every atom has six
immediate neighbours. Figure 6
shows this arrangement for the atoms labeled A. The second
layer is shaded in the figure. It has the same plane-triangular
structure; the atoms sit in the holes formed by the first layer.
The first layer has two equivalent sets of holes, but the atoms
of the second layer can occupy only one set. The third layer,
labeled C, has the same structure, but there are two
choices for selecting the holes that the atoms will occupy.
The third layer can be placed over the atoms of the first layer,
generating an alternate layer sequence ABABAB .
. . , which is called the hexagonal- closest-packed
(hcp) structure....
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